The present invention relates to a railroad-vehicle truck with a frame that yields under torsion and consists of gantry supports or transoms and sole bars or side frames welded into an H, with the transoms also yielding under torsion.
Trucks that yield under torsion and have a central portion consisting essentially of two transoms (I sections for example) that yield under torsion and are welded to side frames that also yield under torsion, at least in the area between the transoms, are known. The area demarcated by the central portions of the transoms and side frames is reinforced with a transverse brace to increase the diagonal rigidity of the frame.
The ends of the sole bars in trucks without buffer beams are constructed to resist torsion and hence in the form of closed sections for instance. The side frames in trucks with buffer beams yield under torsion along their total length.
Trucks of the aforesaid type, which yield under torsion, are described for example in British Pat. No. 1,252,936 and U.S. Pat. No. 4,279,202.
The space for accommodating a truck of the aforesaid type is so limited in many practical cases, however, as to make them impossible to employ.
The maximum permissible axle base, wheel diameter, and space taken up by the shoe brake in some known freight-car trucks for example are givens. The remaining central portion of the truck is too narrow to allow a long enough torsion section in the middle of the side frame. The consequence is that the torsion of the truck will produce higher material stresses, especially at the transitions between the middle of the side frames, which yields under torison, and their torsion-resistant ends.
This is especially true of the type of truck described in British Pat. No. 1,252,936.
Since a maximum permissible overall height must also be adhered to, making it necessary to employ side frames with a depression, and since the maximum permissible overall length prevents the employment of a buffer beam, the type of truck described in U.S. Pat. No. 4,279,202 must also be ruled out.
A rigid-corner frame that yields subject to torsion is on the other hand a particular advantage in freight-car trucks.
Freight-car trucks with a frame that consists of two side frames that are not joined at a central portion are known. The sole bars are kept separate by the wheel sets, and the helical compression springs that support the bolster are positioned in an aperture in each side frame. The bolster also extends into the aperture. Vibration is accommodated in these trucks by means of spring-loaded wedges between the bolster and the truck frame. This type of truck includes those with constant swing restriction and those with load-dependent swing restriction.
The decisive drawback to this type of truck is the lack of corner rigidity. The right angle between the midline of the side frame and the wheel set can deform into a parallelogram when the train travels over a curve, through a point, or in general past any irregularity in the track. This leads to increased load on the wheel flanges and hence to higher wear and a greater tendency to derail. A structure of this type also tends to run unstably (zig-zag) even at low speeds.
The known trucks also have other drawbacks.
The spring-support base must equal that of the axle bearings, and the transverse stop between the bolster and the side frames must be approximately as high as the center of the wheel set to prevent the axle bearings from going askew or even the sole bars going aslant with respect to its longitudinal axis.
Since the transverse stop is a component of the bolster, the bolster is positioned directly above the center of the axle and the springs essentially under it. The low position of the springs (increased distance from the center of gravity of the car) and the relatively small bearing distance have a deleterious effect on the rolling stability of the vehicle.